The present invention relates to systems and methods for the treatment of the spine, and especially the interbody disc space. More specifically, the invention concerns the injection of a biomaterial into a spinal space, such as the intradiscal space.
Spine fusion procedures represent the state of the art treatment for intervertebral disc problems, which generally involve open surgery and the use of interbody fusion cages and spinal fixation systems to stabilize the fusion site. An alternative treatment under evaluation is to replace the disc or nucleus pulposus with a prosthetic device. Examples of some devices currently under investigation include in-situ cured polymers such as polyurethanes and protein polymers, which may have properties varying from a rubbery hydrogel to a rigid plastic. Problems associated with these devices occur during insertion, whereby the pressure required to fill the disc space can cause leakage of the material into sensitive adjacent areas.
A number of devices are available for distracting vertebral bodies or for injecting material into the disc. Some devices are capable of both distraction and injection using the same instrument. These types of devices use a deflated balloon attached to a cannula and inserted between the vertebral bodies. The balloon is inflated with a prosthetic fluid through the cannula to distract the vertebral bodies. This requires high-pressure delivery of the fluid to achieve the pressure needed to distract the vertebral bodies and the balloon and fluid permanently remain in the disc space. Alternatively, a separate device is used to inject the prosthetic fluid around the balloon and the balloon is used strictly for distraction after which it is deflated and removed.
U.S. Pat. No. 4,772,287 (“Ray I”) discloses a bladder injected with thixotropic gel implanted between two vertebral bodies to restore the disc height. The technique described requires that the vertebral bodies are first distracted and a bore drilled to allow for insertion of the bladder.
U.S. Pat. No. 5,562,736 (“Ray II”) discloses a method for implanting a prosthetic disc nucleus. Ray II discloses cutting a first and second flap in the annulus. The flaps provide access to the nucleus. Ray II then discloses using an inflatable jack to distract the disc space prior to insertion of the prosthetic spinal disc nucleus. The jack has a deflated balloon on its end that is inserted into the nucleus through one of the flaps. The balloon is inflated with fluid causing the vertebral bodies to distract. Once the vertebral bodies are sufficiently distracted the fluid flow is stopped and the prosthetic spinal disc nucleus is inserted through the other flap. The balloon is then deflated and the second prosthetic spinal disc nucleus is inserted. The flaps are closed and placed in contact with the annulus by a suture, staple or glue.
U.S. Pat. No. 6,187,048 (“Milner”) discloses an implant for an intervertebral disc nucleus pulposus prosthesis made from a conformable, in-situ curable, material which is resiliently deformable. Milner discloses removing the nucleus material, then either injecting through the annulus or creating an opening in the annulus to deliver a curable material under pressure into the nucleus space. The pressure is necessary to ensure conformation to the nucleus space and/or to increase the internal pressure of the disc space to distract the vertebral bodies. The amount of pressure needed to distract the disc space is high and may allow the material to flow through cracks or voids in the annulus into the disc space. Milner also describes an embodiment where the curable material is injected into a flexible container that is inserted first into the nucleus space in a deflated state and inflated by the material as the material is injected. This method relies on the pressure of the fluid as it is injected to distract the vertebral bodies. Although this avoids the problem of the material leaking through the annulus, it imposes certain constraints such as a designing a cover of the correct shape and size suitable for safe injection of the curable material and prevention of leakage of the material from the cover once filled.
U.S. Pat. No. 6,248,131 (“Felt”) describes distracting and injecting at the same time using a balloon device. The balloon can be used as a shell for containing the injected curable biomaterial and also used as a distraction means as the material is injected. Another embodiment describes the balloon as a cylinder shape which when inflated inside the disc space bears against the endplates for the vertebral bodies and distracts them. Then a second device is used to inject the curable biomaterial around the balloon cylinder. The material is allowed to cure and then the balloon is removed and a second curable biomaterial can be injected into the space left where the balloon was. In sum, when Felt discloses injecting material outside of the balloon, Felt discloses using a second device to carry out the injection. Insertion of this second device into the disc should typically require a second breach of the annulus fibrosis.
Much of the prior art contemplates free injection of biomaterial into a spinal space which may lead to uncontrolled leakage. The art also describes injection of the material into a deflated balloon, which requires leaving the balloon inside the disc space. Lastly, some methods require insertion under high pressure, thereby creating a potential for the prosthetic fluid to ooze or seep out of the disc space intra-operatively.
There is therefore a need for a system and method for introducing a biomaterial into a spinal space that is not prone to the problems of the prior art, especially the leakage problem experienced by the high pressure injection systems. This need extends to systems that can be easily utilized in a minimally invasive procedure.